1. Technical Field of the Invention
The present invention relates generally to a gas sensor which may be installed in an exhaust system of an internal combustion engine for air-fuel ratio control, and more particularly to an improved structure of an electric connector used in such a gas sensor.
2. Background Art
EP0506897 discloses a typical laminated gas sensor. This sensor has the disadvantage that a structure for providing a sensor signal to an external device is complex and results in instability of the sensor signal. The present invention is directed to an improved structure of a gas sensor which is capable of outputting a sensor signal accurately.
An oxygen concentration measuring gas sensor, as will be described below in detail, may be proposed as being installed in an exhaust system of an internal combustion engine for air-fuel ratio control.
The gas sensor includes a sensor element, a sensor element side insulation porcelain, an atmospheric side insulation porcelain, a hollow cylindrical housing, and an atmospheric cover. The sensor element side insulation porcelain is made of a cylindrical member and retains therein the sensor element. The atmospheric side insulation porcelain is disposed in alignment with the sensor element side insulation porcelain to cover a base portion of the sensor element. The housing retains therein the sensor element side insulation porcelain. The atmospheric cover is disposed on a base end of the housing to surround the atmospheric side insulation porcelain.
The atmospheric side insulation porcelain has disposed therein a plurality of leads 16, as shown in FIG. 17, connected electrically with the sensor element. Each lead 16 is coupled through a hollow connector 92 electrically to a lead 17 extending outside of the gas sensor.
Each lead 16 is, as clearly shown in FIG. 16(b), inserted into one of the connectors 92 from an end 920, while each lead 17 is, as shown in FIG. 17, inserted into the connector 92 from the other end in alignment with the lead 16. Each of the connectors 92 is, as clearly shown in FIG. 16(a), made of a flat plate bent to a rectangular shape in cross section which is smaller than holes 322 formed in the atmospheric side insulation porcelain 32.
The above structure, however, encounters the drawback in that the connectors 92 may, as shown in FIG. 17, drop partly into the holes 322, which leads to a difficulty in pressing and welding desired portions of the connectors 92 to join them to the leads 16. This problem may be avoided by decreasing the diameter of the holes 322, but it will result in a difficulty in passing the leads 16 through the holes 322. The holes 322 also work as a reference gas induction passage for supplying a reference gas (i.e., air) into a reference gas chamber. The decrease in diameter of the holes 322, thus, also results in a decrease in amount of the reference gas admitted into the reference gas chamber.
It is therefore an object of the invention to provide an improved structure of an electric connector of a gas sensor which is designed to ensure the reliability of electric connection between a sensing element and an external device.
According to one aspect of the invention, there is provided a gas sensor which comprises: (a) a hollow cylindrical housing; (b) a sensing element having a length which includes a sensing portion and a base portion, the sensing element being retained in the housing with the base portion projecting from the housing; (c) a hollow insulating member provided so as to surround the base portion of the sensing element, the insulating member having a wall in which holes are formed; (d) a cover covering the insulating member; (e) first leads each having a first end portion and a second end portion, each of the first end portions being in electric contact with the sensing element within the insulating member, each of the second end portions passing through one of the through holes and projecting outside the insulating member; (f) second leads each having a first end portion and a second end portion, the first end portion extending outside of the gas sensor for electric connection with an external device; and (g) connectors establishing electric connections between the first leads and the second leads, respectively, each of the connectors having a lead joint portion and a stopper, each of the lead-joint portions electrically joining the second end portion of one of the first leads and the second end portion of a corresponding one of the second leads, each of the stoppers being placed in contact with the wall of the insulating member.
In the preferred mode of the invention, each of the stoppers is provided by an extension formed on an end of one of the connectors.
Each of the stoppers may be provided by a portion of one of the connectors which extends outward.
Each of the stoppers may have a tapered end wall for ease of insertion of the second end portion of one of the first leads.
Each of the stoppers may have walls which define a rectangular shape in cross section and have ends expanding outward so that the ends are placed outside one of the holes of the insulating member in contact with the wall of the insulating member.
Each of the connectors may have a longitudinal slit formed therein.
The first leads and the second leads are joined to the connectors by pressing the lead-joint portions of the connector to plastically deform them or welding or soldering the lead-joint portions of the connectors and the first and second leads together.
According to the second aspect of the invention, there is provided a gas sensor which comprises: (a) a hollow cylindrical housing; (b) a sensing element having a length which includes a sensing portion and a base portion, the sensing element being retained in the housing with the base portion projecting from the housing; (c) a hollow insulating member provided so as to surround the base portion of the sensing element, the insulating member having a wall in which holes are formed; (d) a cover covering the insulating member; (e) first leads each having a first end portion and a second end portion, each of the first end portions being in electric contact with the sensing element within the insulating member, each of the second end portions passing through one of the through holes and projecting outside the insulating member; (f) second leads each having a first end portion and a second end portion, the first end portion extending outside of the gas sensor for electric connection with an external device; (g) connectors establishing electric connections between the second end portions of the first leads and the second end portions of the second leads, respectively; and (h) stoppers provided on one of the second end portions of the first leads in contact with the wall of the insulating member.
In the preferred mode of the invention, each of the connectors may have a longitudinal slit formed therein.
The first leads and the second leads are joined to the connectors by pressing the lead-joint portions of the connector to plastically deform them or welding or soldering the lead-joint portions of the connectors and the first and second leads together.
According to the third aspect of the invention, there is provided a gas sensor which comprises: (a) a hollow cylindrical housing; (b) a sensing element having a length which includes a sensing portion and a base portion, the sensing element being retained in the housing with the base portion projecting from the housing; (c) a hollow insulating member provided so as to surround the base portion of the sensing element, the insulating member having a wall in which holes are formed; (d) a cover covering the insulating member; (e) first leads each having a first end portion and a second end portion, each of the first end portions being in electric contact with the sensing element within the insulating member, each of the second end portions passing through one of the through holes and projecting outside the insulating member; (f) second leads each having a first end portion and a second end portion, the first end portion extending outside of the gas sensor for electric connection with an external device; (g) connectors establishing electric connections between the second end portions of the first leads and the second end portions of the second leads, respectively; and (h) stoppers provided in contact with the wall of the insulating member to hold the connectors above the holes of the insulating member.
In the preferred mode of the invention, each of the connectors has a longitudinal slit formed therein.
The first leads and the second leads are joined to the connectors by pressing the lead-joint portions of the connector to plastically deform them or welding or soldering the lead-joint portions of the connectors and the first and second leads together.
According to the fourth aspect of the invention, there is provided a gas sensor which comprises: (a) a hollow cylindrical housing; (b) a sensing element having a length which includes a sensing portion and a base portion, the sensing element being retained in the housing with the base portion projecting from the housing; (c) a hollow insulating member provided so as to surround the base portion of the sensing element, the insulating member having a wall in which holes are formed; (d) a cover covering the insulating member; (e) first leads each having a first end portion and a second end portion, each of the first end portions having a shoulder and being in electric contact with the sensing element within the insulating member, each of the second end portions passing through one of the through holes and projecting outside the insulating member; (f) second leads each having a first end portion and a second end portion, the first end portion extending outside of the gas sensor for electric connection with an external device; (g) connectors establishing electric connections between the second end portions of the first leads and the second end portions of the second leads, respectively; and (h) stoppers each provided by an extension formed on an end of one of the connectors, placed in contact with the shoulder of the first end portion of one of the first leads to hold the one of the connector.
In the preferred mode of the invention, each of the connectors has a longitudinal slit formed therein.
The first leads and the second leads are joined to the connectors by pressing the lead-joint portions of the connector to plastically deform them or welding or soldering the lead-joint portions of the connectors and the first and second leads together.